1. Field of the Invention
The invention concerns film deposition apparatus and, more precisely, it concerns chemical vapor deposition (CVD) apparatus with which thin films are deposited on a substrate by means of a vapor-phase reaction invoked by plasma or heat.
2. Description of Related Art
Progress has been made with the integration and miniaturization of elements in the field of semiconductor manufacturing apparatus in recent years. The miniaturization of elements has required new techniques in the manufacturing process. For example, it has been necessary to achieve the full-filling with film of fine holes such as via holes and through holes, to reduce steps within an element and to prevent wiring breakdown due to electro-migration or heating caused by high current densities.
Sputtering cannot fulfill these requirements at the present time. With the miniaturization of holes in particular, sputtering has poor step coverage properties for fine holes. Attention has focused on plasma enhanced CVD and thermal CVD in recent years as replacements for sputtering.
Plasma is used for the chemical reaction in plasma enhanced CVD, and heat is used in thermal CVD. These types of CVD can uniformly full-fill with film right through to the base of fine holes which have a large aspect ratio. The Ti films or TiN films obtained with TiCl4 as the source gas which are used as barrier films to prevent diffusion are examples of deposition using plasma enhanced CVD. The blanket tungsten (B-W) films used for wiring purposes are an example of deposition using thermal CVD.
An example of conventional plasma enhanced chemical vapor deposition (PECVD) apparatus for Ti film or TiN film deposition is described below with reference to FIG. 4. The air-tight reactor 111 is furnished with the substrate holder 112 in the center of the lower part and with the disk-like reaction gas delivery part 113 in the upper part. The substrate holder 112 and the reaction gas delivery part 113 face one another and are roughly parallel to one another. The reaction gas delivery part 113 has gas discharge holes formed in its lower surface. The gas discharge holes are connected to the reaction gas supply mechanism 114 which is located outside the reactor 111. The reaction gas delivery part 113 is fixed via the ring-shaped insulator 116 to the upper wall 115 of the reactor 111. The gas delivery part 113 and the reactor 111 are electrically insulated by the ring-shaped insulator 116. The reactor 111 is grounded and maintained at the ground potential. On the other hand, the reaction gas delivery part 113 is connected to the high frequency (HF) source 118 via the matching circuit 117 and supplied with high frequency (HF) power.
A plurality of exhaust ports 119 are formed in the bottom wall of the reactor 111. The exhaust ports 119 are connected to the pumping mechanism 120. The interior of the reactor 111 is maintained at a prescribed pressure by reducing the pressure by means of the pumping mechanism 120.
The substrate holder 112 is fixed to the bottom wall of the reactor 111. The substrate holder 112 is grounded. The electrostatic chuck (ESC) plate 121 is established on the upper surface of the substrate holder 112. The ESC plate 121 is connected to the electrostatic chuck (ESC) control source 122. The substrate 123 which has been located on the substrate holder 112 is clamped by means of the ESC plate 121. The heater 124 is arranged within the substrate holder 112, and the thermocouple 125 which has a temperature detecting function is also provided. The detection signal from the thermocouple 125 is input to the heating control mechanism 126, and the control signal put out from the heating control mechanism 126 is applied to the heater 124.
The substrate 123 which has been transferred into the reactor 111 is arranged on the substrate holder 112. The substrate holder 112 is heated and maintained at a fixed temperature by means of the thermocouple 125, the heating control mechanism 126 and the heater 124. The substrate 123 is held by means of the ESC plate 121.
In the case of Ti film deposition H2 is introduced from the reaction gas delivery part 113 which faces the substrate 123, and H.sub.2 and N.sub.2 are introduced in the case of TiN film deposition. The interior of the reactor 111 is exhausted via the exhaust ports 119 by means of the pumping mechanism 120. In this way the interior of the reactor 111 is maintained at the prescribed pressure. The plurality of exhaust ports 119 are established with a symmetrical positional arrangement so that the flow of gas within the reactor 111 is symmetrical with respect to the center axis of the reactor 111. Moreover, plasma is generated between the reaction gas delivery part 113 and the substrate 123 when HF power is supplied from the HF source 118 to the reaction gas delivery part 113. A frequency from the HF band to the VHF band of from 10 to 100 MHZ is used.
TiCl.sub.4 is introduced from the reaction gas delivery part 113 when the plasma has become stable. As a result, a Ti film or a TiN film is deposited on the heated substrate 123. The unreacted reaction gas and the by-product gas which is produced during film deposition is exhausted via the exhaust ports 119 by means of the pumping mechanism 120.
Reaction gas flow rates of from 2 to 10 sccm TiCl.sub.4, from 300 to 1000 sccm H.sub.2, from 0.2 to 4 sccm SiH.sub.4, and from 10 to 100 sccm N2 (for TiN films only), a substrate holder 112 temperature of from 400 to 700.degree. C., a HF power supply from the reaction gas delivery part 113 of from 50 to 3000 W and a frequency of from 10 to 100 MHZ are typical conditions for Ti or TiN film deposition.
A dead space 127 is formed around the reaction gas delivery part 113 in the vicinity of the upper wall of the reactor 111 in conventional PECVD apparatus, as shown in FIG. 4. The dead space 127 is inevitably produced within the reactor 111 as a result of the design conditions of the apparatus. For example, if a cylindrical reaction gas delivery part is arranged in a rectangular reactor, the space in the corners of the reactor will become a dead spaces 127. If the upper wall and the side wall of the reactor are joined with a hinge so that it can be opened and closed by rotating on the upper wall, the reaction gas delivery part which is fitted to the inside of the upper wall must be smaller than the upper wall. As a result, a dead space 127 is formed around the reaction gas delivery part. The conventional PECVD apparatus shown in FIG. 4 has the distance between the substrate holder 112 and the reaction gas delivery part 113 shortened in order to raise the utilization efficiency of the reaction gas, and the reaction gas delivery part 113 is separated from the wall of the reactor 111 in order to prevent diffusion of the plasma into the space between the wall of the reactor 111 and the reaction gas delivery part 113 which is the upper electrode. These design conditions inevitably result in the formation of the dead space 127.
The dead space 127 is located above the reaction gas flow-way in the conventional PECVD apparatus shown in FIG. 4. The dead space 127 is outside the flow-way of the reaction gas which reaches the exhaust ports 119 from the gas reaction gas delivery part 113. The reaction gas is heated by the hot substrate 123 and so convection of the heated reaction gas around the substrate 123 is liable to occur. The convection around the substrate 123 causes a circulation 128 of reaction gas to occur within the dead space 127 as shown in FIG. 5. As a result, the reaction gas remains in the dead space 127. This behavior of the flow of reaction gas is based on the results obtained from a simulation involving numerical calculations. Such a flow of reaction gas results in the build-up of undesired films on the reactor walls in the vicinity of the dead space 127. This becomes a source of dust particle contamination and has a bad effect on the manufacturing yield in semiconductor production. Here, in this specification, the term "dead space" is defined as a space in which reaction gas is retained.